The present invention relates to paper feeding devices that can be applied in apparatuses such as image forming apparatuses that carry out predetermined processing on sheets such as papers, and particularly relates to paper feeding devices and image forming apparatuses provided with these in which sheets from a loading member in which sheets can be loaded and stacked are supplied to outside the loading member.
Generally a sheet housing portion, such as a paper feeding cassette or a paper feeding tray accommodating a plurality of sheets, is installed in a paper feeding portion in apparatuses such as image forming apparatuses that carry out predetermined processing on sheets. The paper feeding device is provided in a paper feeding portion, and this paper feeding device is provided with a paper feeding mechanism that supplies the sheet positioned at an uppermost portion of the sheets housed in the sheet housing portion in order sheet by sheet toward a transport path.
Ordinarily, a loading member in which sheets can be loaded is provided in the paper feeding device to facilitate the feeding of the sheets by the paper feeding mechanism.
In this regard, when sheets such as papers are left exposed to open air (for example, when loaded in the sheet housing portion), the sheets sometimes curl (for example, they may curl such that end portions gradually become higher than central portions in a sheet transport direction) due to the effect of humidity or temperature or the like. When this happens, the following problems may occur.
In ordinary ambient environment conditions (for example, a low temperature and low humidity (more specifically, 10° C., 20% RH) or a high temperature and high humidity (more specifically, 30° C., 85% RH)), sheets such as papers tend to curl easily. In particular, in cases where curling has occurred in sheets having a certain thickness having a basis weight (grammage) of 100 g/m2 or greater such as firm cardboards and glossy papers or the like, problems occur of sheet blockages (hereinafter referred to as jamming).
Hereinafter, description is given regarding problems caused by sheet curling using as an example a case in which a rotating board is used as the loading member.
In this case, the rotating board is rotatable around an axis along a horizontal direction orthogonal to the sheet transport direction. Mechanisms that are known for moving this rotating board include for example a mechanism in which the rotating board is rotationally moved upwards using a drive portion such as a lift up motor so that an area near a sheet transport direction downstream side end portion (hereinafter referred to as leading edge portion) of the sheets accommodated in the sheet housing portion is biased upwards (see JP H06-87543A and JP H07-187452A).
And although JP 2002-104677A (hereinafter referred as patent document 3) discloses a paper feeding device configured such that skewing or faulty paper feeding tends not to occur even with curled papers, it can hardly be said that this paper feeding device is capable of reliably preventing paper feeding problems caused by curling.
FIGS. 8A and 8B and FIGS. 9A and 9B are schematic views for describing a paper feeding device described in patent document 3. FIG. 8A shows a state in which sheets P, which are not curled, have been lowered within a sheet housing portion 80 and FIG. 8B shows a state in which the uncurled sheets P are being transported after being raised in the sheet housing portion 80. Furthermore, FIG. 9A shows a state in which sheets P, which have curled, have been lowered within the sheet housing portion 80 and FIG. 9B shows a state in which the curled sheets P are being transported after being raised in the sheet housing portion 80. It should be noted that the dashed line in FIG. 9B shows a transport trajectory of the sheet P leading edge.
In a paper feeding device 200′ described in patent document 3, when an elevator platform 201′ is caused to rotate from the state shown in FIG. 8A so as approach a first paper feeding roller 202 and a bundle of regular (not curled) sheets P is raised by the elevator platform 201′, an uppermost positioned sheet P contacts the first paper feeding roller 202, and when the sheets P are further raised, a coupled portion detector piece 207a of a moving member 207 blocks the light of a photoelectric sensor 208, and the raising of the sheets P stops as shown in FIG. 8B. Then, the first paper feeding roller 202 feeds out the sheet P from the sheet housing portion 80 to a nip portion γ between a second paper feeding roller 203 and a separator roller 204, and the sheets P are transported sheet by sheet.
On the other hand, in the case where the sheets P have curled due to the effect of humidity or temperature or the like, when the bundle of curled sheets P is raised by the elevator platform 201′ from the state shown in FIG. 9A, the sheets P make contact with a contact portion 207b of the moving member 207 that is separate from the first paper feeding roller 202 as shown in FIG. 9B, and when the sheets P are further raised, the coupled portion detector piece 207a of the moving member 207 blocks the light of the photoelectric sensor 208, and the raising of the sheets P stops. Due to the raising of the sheets P being hindered in this manner in response to the curled state of the sheets P, when the sheets P are to be supplied from the first paper feeding roller 202 to the nip portion γ between the second paper feeding roller 203 and the separator roller 204, their width direction side ends do not make contact with or do not make strong contact with an upper portion guide 205 that is secured in the device main unit (see the dashed dotted line in the diagrams).
However, when a transport guide member 206 is provided between the first paper feeding roller 202 and the second paper feeding roller 203, for example to smoothly guide the sheets P from the first paper feeding roller 202 to the second paper feeding roller 203, at least a portion of the transport guide member 206 may be positioned below the upper portion guide 205, which is intended to prevent contact of the sheets P. When this happens, in the paper feeding device described in patent document 3, although contact of the sheets P to the upper portion guide 205 can be prevented as shown in FIG. 9B, during transport of the sheets P, the sheets P may make contact with the portion of the transport guide member 206 that is positioned below the upper portion guide 205 (see the α portion in FIG. 9B), and when a leading edge portion P1 of the curled sheet P is transported while making contact with the transport guide member 206 in this manner, paper feeding problems may occur such as paper feeding delays due to reductions in the transport force caused by frictional load at the contact portion a between the sheet P and the transport guide member 206 or jamming due to obstruction of the leading edge portion of the sheet P.